1. Field of the Invention
The invention relates to a device for preventing printing unit damage in the event of a printing stock web tear in a roll-fed rotary printing machine. The device of the present invention has capture cylinders arranged on both sides of the printing stock web (paper web), which are driven at approximately machine speed and are urged against each other by a resilient member during normal operation as well as in the event of a tear.
2. Description of the Related Art
A prior art device of this type is known from DE 33 09 558 A1. This prior art device discloses the use of two capture cylinders urged against each other on opposing sides of the paper web. In the prior art device, at least one of the two capture cylinders is covered with a rubber blanket for absorbing ink. The capture cylinders, because they are positioned against each other at all times, during both normal operation as well as in the event of a web tear, improve the print quality as follows: After several rotations, the rubber blankets on the capture cylinders become inked in the pattern of the printed image, so that printing ink is re-split from the rubber blankets onto the paper web in keeping with the printed image. As a result, the irregularities in ink coverage that normally occur in the printing units are compensated for during consecutive capture cylinder rotations. The fact that the capture cylinders become inked after several rotations also serves to improve the winding of a torn web around one of the cylinders in the event of a tear in the paper web, because the printing ink that adheres to the cylinders attracts the torn paper web, causing the paper web to cling to the rubber blanket and thereby facilitating reliable winding of the paper web.
A problem with this prior art is that it has been found that some contamination of the paper web still occurs because a buildup of the printing ink adhering to the capture cylinders transfers to the printing stock web.